In an electronic valve actuation (EVA) engine, the intake valve timing may be controlled on a cylinder by cylinder basis. In one example configuration, the intake valves may be controlled by a separate valve control unit (VCU), sometimes referred to as a valve controller, that responds to valve timing commands from the engine control module (ECM) by opening and closing the intake valves in a manner that is synchronized with the application of spark and fuel timing. One issue with using a VCU that operates separately from the ECM is in maintaining synchronization between the two control modules. In particular, during operation, the VCU internal clock may become time shifted from the ECM clock which may result in reduced intake valve control accuracy.
One approach for addressing this issue is to send synchronization messages between the ECM and the VCU via a control area network (CAN). However, the inventors have recognized some short-comings with this approach. For example, the ECM may be configured to send event based messages (i.e., messages that are related to some physical engine event) over a CAN link to the VCU once every 90 crank angle degrees. If the VCU also uses event based CAN messaging then it may not be possible to measure a synchronization error of less than the event spacing, i.e., 90 crank angle degrees. Further, even if the VCU uses an interrupt service routine or a polling system that is not based on event based messaging, variations in CAN message timing may lead to synchronization errors between an ECM and VCU.
One example approach to overcome at least some of the disadvantages of the prior approach includes sending an engine position indication signal from a first controller to a second controller over a first link, sending a status signal from the second controller to the first controller over a second link, and synchronizing the second controller and the first controller according to the engine position indication signal and the status signal.
In a second approach, also described herein, the above short-comings may be addressed by a system with at least one cylinder with an engine cylinder valve, a second controller operably coupled to the engine cylinder valve, the second controller configured to adjust at least one of the valve opening and closing timing of the engine cylinder valve, and a first controller connected with the second controller over a first link and a second link, wherein the first controller is configured to send an engine position indication signal to the second controller over the first link and receive a status signal from the second controller over the second link, and wherein the first controller outputs a synchronization degradation signal responsive to a synchronization error between the engine position indication signal and the status signal.
The present description provides several advantages. In particular, if an engine position indication signal, such as a composite top dead center (TDC) signal degrades, e.g. less than a complete data set is received than is transmitted, then a VCU to ECM synchronization error can be calculated by comparing an internal ECM TDC edge timing to the VCU status signal edge timing. Additionally, if the VCU status signal degrades then a synchronization error can be calculated within the VCU by comparing its TDC timing with the composite TDC signal edge timing, and then the synchronization error can be transmitted to the ECM over the CAN link for engine control purposes. Further, in the case that both the composite TDC and VCU status signals degrade, a cylinder ID timing can be transmitted from the VCU to the ECU, with sufficient resolution to provide an additional means of detecting VCU to ECM synchronization errors.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.